Generally, for the spray coating of an object having a comparatively large coating surface, like a body of an automobile, furniture or electrical appliances, a coating method has been known to perform coating the coating surface of the object is divided into a plural number of segments (see, for example, Japanese Patent Laid-Open No. Hei 9-52067 and Hei 2003-144990).
Disclosed in Japanese Patent Laid-Open No. Hei 9-52067 is an arrangement to provide two sprayer units at right and left end sides of the body of an automobile, and the upper surface of the vehicular body is coated after being divided into right and left coating areas. According to the arrangement in this case, the two sprayer units are reciprocated laterally of the vehicular body, coating individual coating areas, and return to the boundary between the two coating areas. At this time, since the spray patterns of the two sprayer units interfere with each other at the boundary of the coating areas, the coating film is thicker than at other coated portions, and this causes a coating failure, such as color shading. Therefore, according to the prior art in cited patent literature 1, at the boundaries of the coating areas, where the spray patterns of the two sprayer units interfere with each other, the sprayer units are gradually away from the coating surface to prevent an excessive increase in the thickness of the coated film.
On the other hand, according to an arrangement described in Japanese Patent Laid-Open No. 2003-144990, to prevent an increase in the thickness of a coated film at the boundaries of coating areas, the positions of the turning paths for reciprocation are alternately shifted to the right and to the left to form coating trajectories having a comb-toothed shape. Further, the spray of paint by the individual sprayer units is cut at the turning paths.
Then, factors related to the finished coating properties, such as the number of laminations of spray patterns and the thickness of the coated film, are different between portions that the sprayer units are moved parallel (parallel transit paths) during reciprocation and the turning paths for the reciprocation of the sprayer units. Therefore, in the prior art, at the turning paths for the reciprocation of the sprayer units, factors related to finished coating properties, such as the timing for the supply of paint and the stop of the supply (ON and OFF), the size of the spray pattern, the discharge quantity and the coating distance, are compoundly changed in order to obtain a uniform quality for the finished coating across the entire surface.
However, according to the coating method described in Japanese Patent Laid-Open No. Hei 9-52067, the sprayer units are away from the coating surface at the turning paths for the reciprocation of the sprayer units. Therefore, the spray pattern is extended, compared with the parallel transit path. As a result, the coated film has a uniform thickness, however color shading tends to occur.
Furthermore, according to the coating method described in Japanese Patent Laid-Open No. 2003-144990, although substantially the same spray pattern as in the parallel transit path can be used at the turning paths, the coated film thereat tends to be thicker than in the parallel transit path because the coating trajectories, which have comb-toothed shapes overlap each other at the boundaries of the two coating areas. As described above, according to the prior art, the finished coating quality across the entire coated surface can not always be appropriately uniform.
Especially, for the deposition of a coated film, a so-called metallic paint that contains a high luminance pigment, such as mica powder or aluminum powder, greatly influences the finish of a coat. Thus, when a metallic paint is employed, a problem is occurred that deterioration of the finished coating is noticeable at the turning paths at the boundaries of adjacent coating areas, and accordingly, the finished coating quality tends to be reduced across the entire coated surface.